National Geographic writer and explorer Dan Buettner studies the world's longest-lived peoples and their lifestyles. Courtesy TEDxTC hide caption

itoggle caption Courtesy TEDxTC

Village chiefs, residents and government officials take to the streets to celebrate the Chienge district's accomplishment of bringing sanitation to every home. Mark Maseko/Courtesy of UNICEF Zambia hide caption

itoggle caption Mark Maseko/Courtesy of UNICEF Zambia

The Ebola outbreak "overwhelmed" the World Health Organization and made it clear the agency must change, WHO's director-general, Dr. Margaret Chan, said Monday in Geneva. Fabrice Coffrini /AFP/Getty Images hide caption

itoggle caption Fabrice Coffrini /AFP/Getty Images

Jenny Tenorio Gallegos, 35, in Lima, Peru, is being treated for drug-resistant TB. The treatment lasts two years and may rob her of her hearing. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

Families harvest poppy bulbs in the Badakhshan province of Afghanistan. To collect the opium, they score the bulbs and let the milky substance ooze out. The dried residue contains about 10 percent morphine. David Guttenfelder/AP/National Geographic hide caption

itoggle caption David Guttenfelder/AP/National Geographic

Researchers meet participants: (from left) investigator Jose Luis Roca; Dr. Ernesto Ortiz; study participants Rainer Leon and his mother, Rina Leon Chanbilla; and nurse Jennifer Rampas. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

Kids in Cape Town socialize as they walk to school. Children in South Africa often don't get to play outside by themselves because of the high rate of violent crimes in some areas. Henk Badenhorst/Getty Images hide caption

itoggle caption Henk Badenhorst/Getty Images

This aerial view shows the effects of gold mining on Peru's rain forest. Courtesy of Gregory Asner, Carnegie Institution for Science hide caption

itoggle caption Courtesy of Gregory Asner, Carnegie Institution for Science

A boot-drying rack sits empty at the Ministry of Defense Ebola Treatment Unit in Monrovia. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

Moses Lasana recovered from Ebola, but he faces a range of medical issues and waves of pain. "The pain just come from one part of the body to another," he says. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

More than 1 million people in Peru earn less than the equivalent of about $450 each year. Courtesy of Michael Rizzo/CGAP hide caption

itoggle caption Courtesy of Michael Rizzo/CGAP
Corbis

In a study in Lesotho, the prospect of earning a cash prize in a lottery motivated young people to practice safe sex. iStockphoto hide caption

itoggle caption iStockphoto